fix: make Register-CfsFeed robust to non-terminating source collision

The 'already added' error is non-terminating and bypasses -ErrorAction Stop (so try/catch never
fires) yet fails the PowerShell task under its default Stop preference. Pre-check Get-PackageSource
(surfaces the collision that Get-PSRepository lazily misses in a fresh session), and suppress all
streams on Register-PSRepository with a post-verify instead of relying on the call to not error.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 6ea00b50-c719-469b-bf9c-72120184bfe0

Author: gavinbarron

tools/Get-CfsFeedCredential.ps1

@@ -35,21 +35,20 @@ function Register-CfsFeed {
     # Registers the private feed as a Trusted PSRepository (idempotent). Persisted under the user's
     # PowerShellGet config, so a single registration per job is visible to later steps and runspaces.
     $cred = Get-CfsFeedCredential
-    if (Get-PSRepository -Name $script:CfsFeedName -ErrorAction SilentlyContinue) {
+    # Get-PSRepository can lazily return nothing in a fresh session even when the source is already
+    # persisted (registered by an earlier step/runspace). Get-PackageSource surfaces that collision,
+    # so check both before attempting to register.
+    if ((Get-PSRepository -Name $script:CfsFeedName -ErrorAction SilentlyContinue) -or
+        (Get-PackageSource -Name $script:CfsFeedName -ErrorAction SilentlyContinue)) {
+        Write-Host "Package source '$($script:CfsFeedName)' is already registered; skipping."
         return
     }
-    try {
-        Register-PSRepository -Name $script:CfsFeedName -SourceLocation $script:CfsFeedUrl -InstallationPolicy Trusted -Credential $cred -ErrorAction Stop
-    }
-    catch {
-        # A package source with this name may already exist at the PackageManagement layer (e.g. a
-        # NuGet source, or a registration from an earlier step/runspace) that Get-PSRepository does
-        # not surface. If a usable PSRepository now exists, the registration effectively succeeded, so
-        # swallow the "already added" collision; otherwise rethrow the real failure.
-        if (Get-PSRepository -Name $script:CfsFeedName -ErrorAction SilentlyContinue) {
-            Write-Host "PSRepository '$($script:CfsFeedName)' is already registered; continuing."
-            return
-        }
-        throw
+    # The "already added" collision is a non-terminating error emitted by an internal PackageManagement
+    # cmdlet that bypasses -ErrorAction Stop (and would otherwise fail the task under its default Stop
+    # preference), so redirect every stream to null and verify the outcome instead of trusting the call.
+    Register-PSRepository -Name $script:CfsFeedName -SourceLocation $script:CfsFeedUrl -InstallationPolicy Trusted -Credential $cred -ErrorAction SilentlyContinue *> $null
+    if (-not (Get-PSRepository -Name $script:CfsFeedName -ErrorAction SilentlyContinue)) {
+        throw "Failed to register PSRepository '$($script:CfsFeedName)'."
     }
+    Write-Host "Registered PSRepository '$($script:CfsFeedName)'."
 }